In an electrophotographic apparatus or an electrostatic recording apparatus, a two-component developing system method using toner and a carrier and a monocomponent developing system method using toner which also functions as a carrier are extensively used to visualize an electrostatic latent image formed on an image carrier made of a photoreceptor or a dielectric material.
These developing methods include methods using nonmagnetic toner and magnetic toner.
As magnetic toner, Jpn. Pat. Appln. KOKAI Publication No. 1-40976 has disclosed one-component magnetic toner which contains, in toner particles, about 20 to 60 wt % of an iron oxide magnetic particle in which the FeO content, the number-average particle size, and the specific surface area are restricted to 16 to 25 wt %, 0.2 to 0.7 .mu.m, and 2 to 10 m.sup.2 /g, respectively. Jpn. Pat. Appln. KOKAI Publication No. 1-40976 describes that when image formation is performed using this magnetic toner, a high developing efficiency and a high transfer efficiency can be obtained.
A magnetic material used herein has a high degree of blackness as a black pigment and can hold an appropriate electrical resistance. Hence, the material stabilizes the toner charge amount and can thereby improve image density. Also, in respect of developing properties, the material improves the rank of fog on image. However, with recent increasing speed of copying machines, magnetic toner cannot well satisfy high resolution, high durability, and the like any longer. Especially in a low-temperature, low-humidity environment, the charge amount cannot be properly controlled. A lowering of image density and background contamination resulting from an appropriate increase in charge amount cannot be well controlled.